If $x \bigtriangleup y = xy+3x-y$ and $x \bigtriangledown y = x-8y$, find $1 \bigtriangleup (3 \bigtriangledown -2)$.
Explanation: First, find $3 \bigtriangledown -2$ $ 3 \bigtriangledown -2 = 3-(8)(-2)$ $ \hphantom{3 \bigtriangledown -2} = 19$ Now, find $1 \bigtriangleup 19$ $ 1 \bigtriangleup 19 = 19+(3)(1)-19$ $ \hphantom{1 \bigtriangleup 19} = 3$.